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DUMPON(8) FreeBSD System Manager's Manual DUMPON(8)
NAMEdumpon -- specify a device for crash dumps
SYNOPSISdumpon [-v] special_filedumpon [-v] offDESCRIPTION
The dumpon utility is used to specify a device where the kernel can save
a crash dump in the case of a panic.
Calls to dumpon normally occur from the system multi-user initialization
file /etc/rc, controlled by the ``dumpdev'' variable in the boot time
configuration file /etc/rc.conf.
For most systems the size of the specified dump device must be at least
the size of physical memory. Even though an additional header is added
to the dump, the BIOS for a platform typically holds back some memory, so
it is not usually necessary to size the dump device larger than the
actual amount of RAM available in the machine.
The -v flag causes dumpon to be verbose about its activity.
IMPLEMENTATION NOTES
Since a panic(9) condition may occur in a situation where the kernel can-
not trust its internal representation of the state of any given file sys-
tem, one of the system swap devices, and not a device containing a file
system, should be used as the dump device.
The dumpon utility operates by opening special_file and making a
DIOCSKERNELDUMP ioctl(2) request on it to save kernel crash dumps. If
special_file is the text string: ``off'', dumpon performs a
DIOCSKERNELDUMP ioctl(2) on /dev/null and thus instructs the kernel not
to save crash dumps.
Since dumpon cannot be used during kernel initialization, the dumpdev
variable of loader(8) must be used to enable dumps for system panics
which occur during kernel initialization.
SEE ALSOfstab(5), rc.conf(5), config(8), init(8), loader(8), rc(8), savecore(8),
swapon(8), panic(9)FILES
/dev/{ad,da}?s?b standard swap areas
/etc/rc.conf boot-time system configuration
BUGS
Because the file system layer is already dead by the time a crash dump is
taken, it is not possible to send crash dumps directly to a file.
HISTORY
The dumpon utility appeared in FreeBSD 2.1.
FreeBSD 10.1 May 12, 1995 FreeBSD 10.1